Underneath the bustling streets of Tokyo lies an engineering marvel that few people are aware of: the Kanda River Underground Regulating Reservoir. While walking to the building housing it, I was completely unaware of this hidden giant that plays a crucial role in the city’s flood management system, safeguarding Tokyo from potential water-related disasters.
The Kanda River Underground Regulating Reservoir is an enormous subterranean facility designed to control and manage excess water from the Kanda River. Tokyo, being a densely packed metropolitan area, is particularly vulnerable to flooding due to its compact infrastructure and the prevalence of impermeable surfaces. The Kanda River, which runs through the city’s center, has historically been prone to overflow during heavy rains and typhoons. The Tokyo Metropolitan Government Bureau of Construction began an ambitious project to create this underground reservoir to reduce this risk.
As we went on a guided tour of the facility, we received a detailed explanation of how the reservoir operates as a large storage tank capable of storing 540,000 m³ of water. The guide explained how the underground facility begins taking in water during periods of heavy rainfall when the Kanda River swells with excess water. The system is designed to divert water from the river into the reservoir through a series of tunnels and intake structures, which we observed through a demonstration using a miniature diorama of the facility. Once inside, the water is temporarily stored until the river levels subside, preventing the river from overflowing and flooding the surrounding areas.
The guide explained that after the rainfall event, the stored water is gradually released back into the river, ensuring that the water levels return to normal without causing downstream flooding. They also mentioned that they were exploring the idea of discharging the water into the ocean instead. Either way, a regulated release is crucial in maintaining the balance and preventing sudden surges that could lead to further issues.
The reservoir is also equipped with advanced monitoring and control systems, including sensors and automated gates that help manage water flow in and out. The real-time data collected by these sensors allows for precise control, ensuring that the reservoir operates efficiently and effectively during critical periods.
While I was very interested in learning about how the Kanda River Underground Regulating Reservoir works, I was even more excited to actually see it. We walked down many flights of steps before entering a vast underground chamber that felt like stepping into a different world. The sheer scale of the facility was awe-inspiring, the tunnels being even larger than I imagined. It was hard to believe such an immense structure existed right beneath the city’s surface.
After walking through part of the tunnels and listening to the end of the guided
tour, we returned to the surface and began walking to our next destination. As we were walking, we passed by part of the river that the reservoir monitors. It was remarkable to see the different marks on the wall, signifying when the water level is high enough for the reservoir to be used, and thinking about the complex and extensive system at work beneath our feet.
The significance of the Kanda River Underground Regulating Reservoir cannot be overstated. Tokyo, a city of over 14 million people, is at constant risk of flooding, especially during the typhoon season. The reservoir acts as a critical buffer, protecting both residential and commercial areas from the devastating impacts of floods.
